Zinc compounds, zinc clays and other additives can be used in rubber compounding (e.g., in the manufacture of tires) to obtain desired properties in a finished rubber product. There have been efforts to use zinc montmorillonite clay to replace zinc oxide in rubber compounding to reduce the amount of zinc oxide used in such rubber compounds for both environmental and economic reasons. Such zinc montmorillonite clays are usually made by mixing sodium montmorillonite with zinc chloride to exchange zinc ions with sodium ions in the clay (e.g., as described in PCT/NL2003/000880, the relevant portions of which are incorporated herein by reference). The clay is then washed free of sodium chloride and excess zinc chloride, then dried and milled to form a zinc clay suitable for use as rubber activator.
Organoclays may also used in rubber and plastic compositions as fillers. These organoclay fillers are usually made from smectic clays such as calcium montmorillonite, sodium montmorillonite, saponites, nontronites, beidellites, hecorites, etc. These minerals in turn are dominant parts of bentonite rock. Such clays may be treated with acid, then washed free of the acid and other soluble matter, then converted to their corresponding sodium salts by treatment with soda ash or caustic soda. In one process, a sodium montmorillonite clay is then reacted with quaternary ammonium chloride salts (e.g., dimethyl bis-(hydrogenated tallowalkyl) ammonium chloride) or amines (e.g., laurylamine or tallowalkyl amine) and their salts to form an organoclay. The quaternary ammonium salt intercalates between platelets and/or layers of the clay, helping to expand the interlayer distance in the clay to about 20 angstroms or more. Such intercalation into the clay platelets results in easier exfoliation of the clay during rubber compounding or plastic processing. The exfoliation aids in dispersion of the nanoscale platelets from the clay into various compositions, and imparts various properties like higher hardness, modulus, heat resistance, etc. to products containing such intercalated clays.
It is known that using a zinc soap of a carboxylic acid, dry milled with a layered material of nanoscale thickness, can act as activator in rubber formulations, as mentioned in US Pat. Appl. Publ. No. 2009/0199945 A1. This patent publication uses mostly montmorillonite clay material. Using a zinc clay as described in U.S. patent application Ser. No. 12/577,370 as a starting material, the performance of the layered material can be further improved, especially as a filler for rubber compounds and formulations. It was also discovered that a zinc ammonia carbonate complex solution as described in U.S. patent application Ser. No. 12/577,370 is also an excellent starting material for making the zinc soap layered clay material.
The layers of those clay materials are usually from a few angstroms to about 15 angstroms apart in their natural form. In that form, the layers are difficult to break apart. It is known that if the layers can be intercalated to 20 angstroms or more, it is easier to break apart the clay layers. The D001 parameter is usually used to indicate the largest gap of the platy layers. If it is 20 angstroms or more, the clay layers are more easily broken apart.
Stearic acid and its various metal salts are widely used in the rubber and plastic industries. Stearic acid is also widely available and inexpensive. Stearic acid and its metal salts are also highly compatible with various rubber and plastic formulations, and they can act like quaternary ammonium chlorides on layered clays.